As catalysts used for preparing olefin polymers, e.g. ethylene homopolymer or ethylene/olefin copolymers, there have heretofore been known such titanium-containing catalysts comprising titanium compounds and organoaluminum compounds or vanadium-containing catalysts comprising vanadium compounds and organoaluminum compounds.
Further, as catalysts capable of preparing ethylene/olefin copolymers with high polymerization activity, there have been known olefin polymerization catalysts comprising zirconium compounds and organoaluminum oxy compounds (aluminoxane), and methods for preparing ethylene/olefin copolymer using such catalysts have been proposed, for example, in Japanese Patent L-O-P Publications Nos. 19309/1983, 35005/1985, 35006/1985, 35007/1985, 35008/1985, etc.
Furthermore, Japanese Patent L-O-P Publications No. 260602/1985 and 130604/1985 propose methods for polymerization of olefin using catalysts formed from transition metal compounds and mixed organoaluminum compounds comprising aluminoxane and organoaluminum compounds.
Where it is intended to produce polyolefins having a high molecular weight by using the conventional catalysts as aforesaid, there is proposed a method therefor in which the polymerization is carried out at a relatively low temperature. When the polyolefins high in molecular weight are prepared by such a method just mentioned above, however, it was difficult to prepare polyolefins having high molecular weight with high polymerization activity, because catalyst activity decreases markedly.
As the result of extensive researches conducted by the present inventors in view of the foregoing prior art, they have found that catalysts comprising (A) transition metal compound of the group IVB of the periodic table having a cyclopentadienyl skeleton, (B) organoaluminum oxy compound, (C) at least one kind of carbonyl-containing compound selected from ketoalcohol and .beta.-diketone and, if necessary, (D) organoaluminum compound are capable of polymerizing polyolefin high in molecular weight with high activity, and finally the present invention has been accomplished on the basis of the above findings.
Further, the catalysts formed from transition metal compounds and aluminoxanes as prepared in the foregoing Japanese patent publications are excellent in polymerization activity, particularly polymerization activity on ethylene in comparison with the prior art catalysts formed from transition metal compounds and organoaluminum compounds. However, because the greater part of the proposed catalysts are soluble in reaction system, the application of said catalysts is limited to preparation of polymers by Solution polymerization in most cases, and when polymers high in molecular weight are intended to prepare by using said catalysts, there is brought about such an inconvenience that the solution containing the resulting polymer becomes markedly high in viscosity, whereby the productivity of the intended polymer decreases.
For the purpose of solving such a problem as mentioned above, methods for polymerizing olefins in the suspension or vapor phase polymerization system using catalysts formed from transition metal compound and organoaluminum oxy compound have been proposed, for example, in the foregoing Japanese Patent L-O-P Publications Nos. 35006/1985, 35007/1985 and 35008/1985, wherein at least one of the two catalyst components of said catalysts has been supported on a porous inorganic carrier such as silica, alumina or silica-alumina.
Further, the foregoing Japanese Patent L-O-P Publns. and Japanese Patent L-O-P Publns. Nos. 130314/1986 and 41303/1990 disclose that catalysts systems comprising a combination of metallocene compounds of transition metal compounds having pentadienyl group as ligand such as cyclopentadienyl group, alkyl group and/or halogen atom and aluminoxane exhibit high activity in .alpha.-olefin polymerization, and the polymers obtained thereby are excellent in properties.
Furthermore, Japanese Patent L-O-P Publns. Nos. 108610/1986 and 296008/1986 disclose methods for carrying out olefin polymerization in the presence of catalysts formed from transition metal compounds such as metallocene and aluminoxane, both being supported on a carrier such as inorganic oxide.
However, when olefins are polymerized or copolymerized in the suspension or vapor phase polymerization system using the solid catalyst components supported on the carrier as disclosed in the foregoing patent publications, the polymerization activity expected thereby decreases markedly in comparison with the case of the foregoing solution polymerization system, and no satisfactory result was obtained.
The present inventors conducted extensive researches in view of the prior art as mentioned above, and as a result they have found that supported catalysts formed by supporting catalyst component (A) transition metal compounds of the group IVB of the periodic table containing ligands having a cyclopentadienyl skeleton, (B) organoaluminum oxy compounds and (C) at least one kind of carbonyl-containing compound selected from ketoalcohol and .beta.-diketone and, if necessary, (D) organoaluminum compound, on a solid carrier are excellent in polymerization activity per catalyst unit weight and also are capable of preparing polymers uniform in particle size (there are contained in the resulting polymers few fine powdery polymers), and they have finally accomplished the present invention on the basis of the above finding.